Aromatic aldehydes have aldehyde groups with a high reactivity, so that they may be employed in a wide variety of uses. Especially, terephthalaldehydes having two aldehyde groups at para-positions as Formula 1 below are noted for basic raw materials such as medicinal products, agrichemicals, pigments, liquid crystal polymers, electro-conductive polymers, and heat-resistant plastics.

Said terephthalaldehyde of Formula 1 is a sublimable white solid having a molecular weight of 134.13 and a melting point of 114-116° C. It is known that it is well dissolved in alcohols, and is also dissolved in ethers, alkali solutions and hot water.
Terephthalaldehyde as a raw material of the present invention is prepared by the known methods, which are briefly described below.
In the methods for preparing terephthalaldehyde, there is a method for dehydrating intermediates obtained via chlorination, a method for hydrogenating methylterephthalate, or a method for preparing terephthalate by oxidating p-xylene in vapor phase, etc.
In order to use terephthalaldehyde as a raw material in a polymer synthesis or a fine chemical process, it should be purified to a high purity, for which impurities contained in terephthalaldehyde, such as benzaldehyde, p-tolualdehyde, 4-hydroxybenzaldehyde and the like, have to be removed.
Until now, there is almost no example reported for the method for preparing a high purity terephthalaldehyde which may be used in the polymer synthesis or the fine chemical process by efficiently removing impurities produced in the synthesis of terephthalaldehyde.
U.S. Pat. No. 2,888,488 discloses a method for preparing terephthalaldehyde which includes solvent extracting-drying-subliming as a purification process. This method has, however, problems that its procedures are complicated and a non-environment friendly compound, chloroform, is used as a solvent.
JP Unexamined Patent Publication No. 2001-199910 discloses a method for re-crystallizing aromatic aldehydes by a cooling process. This method is also limited to obtaining a high purity terephthalaldehyde.